Method for distribution of cooling air for electrical equipment installed in an avionic bay and aircraft equipped with such a bay

ABSTRACT

A method for distribution of cooling air for cooling an electrical equipment item installed in an avionic bay. Cooling air is drawn from an air vein, then passes into a first pressure zone in fluidic communication with the air vein and then into a second pressure zone in fluidic communication with both the first pressure zone and the electrical equipment. The second pressure zone extends beneath a largest dimension (e.g., length) of electronic boards of the electrical equipment to be cooled.

CLAIM FOR PRIORITIES

FR Application No. 11 01467 of May 13,2011

This invention relates to a method and a device for distribution ofcooling air for aircraft electrical equipment which in particular isinstalled in an avionic bay. It also relates to a bay able toaccommodate electrical equipment items and an aircraft equipped withsuch a bay.

There are known in the state of the art electrical equipment items madeup of several electronic boards, generally printed circuits on whichheat-dissipating electronic components are installed and soldered.Furthermore, electrical connectors are disposed at least on the edges ofthe boards and the electronic boards as a whole are inserted into ametal housing or packaging. The housing or packaging consists mainly ofa base and a cover. The electrical equipment set up in this way isintended to be installed on a rack of an avionic bay. Avionic bays aredisposed in a pressurized zone of the aircraft, under a partiallycontrolled ambient temperature. These avionic bays provide theelectrical equipment items with preferential ventilation conditions thusallowing cooling thereof.

In order to integrate the electrical equipment items into the avionicbay, there is used, for example, a technique described in the documentU.S. Pat. No. 5,253,484. An avionic bay comprises several racks and eachrack integrates a ventilation vein. On each rack, and for eachelectrical equipment item intended for same, there is installed amechanical and electrical interface, called tray, which performs severalfunctions.

Among these functions, the tray provides aeraulic control of the part ofthe rack above the ventilation vein in which the ventilation airallotted to the electrical equipment items circulates. The cooling airintended for an electrical equipment item is drawn by the tray from thecooling air vein of the rack of the bay. The cooling air is used to drawoff thermal power dissipated by the electronic components of the boardsof the associated electrical equipment. This dissipated thermal power isevacuated through convection by virtue of the cooling air that goesthrough the spaces between the boards before leaving the equipment viaholes provided through the housing of the electrical equipment, thenbeing drawn out of the avionic bay via an extraction shaft situatedabove electrical equipment 2.

Such an arrangement is defined in particular in an internationalaeronautical standard ARINC600 and an exemplary implementation isdescribed in the document US-A 20040050569.

A schematic side view in cross section and a partial view in perspectiveof an electrical equipment item installed on a tray of a rack have beenshown respectively on FIGS. 1a and 1 b.

Rack 1 comprises mainly a bent metal section taking on the shape of achannel bordered by two vertical edges and two side (horizontal) wingsintended to bear electrical equipment items such as equipment 2 lateron.

A tray 9, serving as mechanical and electrical interface, shown inperspective on FIG. 1b , is positioned on the side wings of rack 1. Tray9 has a vertical part 6, forming a back, connected by an angle bracket 6a and an angle bracket 6 b to a horizontal part 7 (FIG. 1b ) forming aseat.

The tray is fastened, for example by screws, onto the side wings of rack1 and is constructed so as to accommodate an electrical equipment item2. The electrical equipment comprises mainly a housing formed by a metalcover which is closed off at the bottom part by a base bearing a slidersupport. On each of the sliders of the slider support, a removableelectronic board such as board 10 on FIG. 1a is inserted.

Electronic board 10 comprises a printed circuit on which there areinstalled a multitude of electronic components arranged in rows 11A, 11Band 11C. A connector 4 makes it possible to connect all the electronicboards of the equipment with an avionic connector not shown on FIG. 1a .The connection is implemented during installation of electricalequipment 2 on tray 9, and during its insertion into an avionicconnector 8 (FIG. 1b ) which is connected to the electrical network ofthe airplane.

As shown on FIG. 1b , seat 7 of tray 9 has, above the channel formed inrack 1 and serving as housing for circulation of a cooling air vein 14,a hollow part 12 which is provided with a plurality of holes such ashole 13. This part constitutes a zone for passage of the air between theventilation vein and the electrical equipment.

As is known in the state of the art and according to the powerdissipated by the electrical equipment, certain holes 13 of seat 7 maybe blocked and others may be open so that the pressure drop between airvein 14 and the flow of cooling air injected into the equipment may becontrolled.

For this purpose, the bottom part of electrical equipment 2 is providedwith slots along the inter-slider spaces. It results from thisarrangement that the cold air is drawn from vein 14 and circulatesvertically on FIG. 1a along the electronic components of the boards thatproduce heat during their operation. The top part 15 of the housing forthe electrical equipment likewise is provided with holes to allowevacuation of the cooling air after its passage over the components tobe cooled.

The inventors became aware that such an arrangement brings about a spacesection part 16 situated to the right of a space section 15 on FIG. 1awhich, in the housing of electrical equipment 2, is not covered by thecooling air. The result is that the electronic board, such as board 10,must be designed so that the zone of this board that is in space section16 of the electrical equipment does not comprise electronic componentscritical from the thermal point of view. This presents a drawback sinceit involves an additional constraint for design of the electronic board.

Furthermore, each manufacturer of electrical equipment items such aselectrical equipment 2 on FIG. 1a is allotted by the designer of theairplane a cooling air flow proportional to the dissipated power so thatthe cooling may take into account the thermal dissipation of theelectronic casings. The ventilation system of the airplane thenmaintains a constant pressure in rack 1 of the electronic bay and eachparts manufacturer is to guarantee that, under the rated flow that isallotted thereto, the pressure drop generated both by the mechanical andelectrical interface tray and by the housing for the actual electricalequipment is:

-   -   250 Pa (+50/−50 Pa); or    -   250 Pa (0/+50 Pa) in constraints more restrictive than the        ARINC600 standard.

In the state of the art, so as to avoid having too many parameters tocontrol in order to determine the pressure drop between vein 14circulating in the rack and the interior of the electrical equipment tobe cooled, the support for the sliders that accommodate the printedboards has extensive cut-outs between these sliders and therefore addshardly any pressure drop. Nevertheless, the seat of the mechanical andelectrical interface tray may be adapted so as to distribute the airextracted between the sliders and the boards installed inside theelectrical equipment item. Such a situation has been shown schematicallyin cross section on FIG. 2. On FIG. 2, the same elements as those ofFIGS. 1a and 1b bear the same reference numbers.

FIG. 2 shows a rack 1 on which an interface tray 9 composed essentiallyof a vertical part or back 6 and a bottom part or seat 7 is installed.

According to the geometry of the rack on the one hand, and the geometryof the electrical equipment on the other hand, the aperture zone 12 islimited in particular by an aeraulic staunch joint 17. Above joint 17there is disposed base 18, the bottom part of the housing for electricalequipment 2 inserted onto tray 9. Base 18 bears a slider support 19 onthe upper face of which a board slider 19′ has been shown. A boardslider 19′ consists of a U-shaped section along which a longitudinaledge of the board not shown on FIG. 2 is disposed. Finally, a closingcover 20 for the electrical equipment is shown in part. Between eachslider 19′ a slot is implemented which makes it possible not tointroduce any additional pressure drop at the lower part of the board.Air is drawn, however, from gaseous vein 14 through aperture zone 12with a controlled pressure drop and passes into sole cooling zone 15. Itis noted that the cooling air cannot go through offset zone 16 which isoffset laterally in relation to zone 15 (zone 16 is not, like zone 15,above aperture zone 12). Zone 16 therefore is unventilated.

The limitation of the ventilation zone to zone 15 penalizes the thermalmanagement of electrical equipment items the front and side zones ofwhich are not directly ventilated. The effect of that is:

-   -   a lack of flexibility as to placement of the components in the        poorly ventilated regions thereof, which is a major constraint        on the architecture of the equipment items as well as during        placement and routing of the components on the boards;    -   this arrangement possibly entails an excessive demand for air in        order to compensate for the lack of cooling in certain zones of        the equipment.

On FIG. 2, the apertures of aperture zone 12 allow an aerauliccommunication between air vein 14 and cooling zone 15 that goes throughslot 21 disposed between each inter-slider space in slider support 19.Since electrical equipment 2 is fully included in cover 20 integral withbase 18, it is noted that the cooling flow is not conveyed tounventilated zone 16 (to the right on FIG. 2) which constitutes thefront zone of the electrical equipment when it is installed in the bay.

In order to remedy at least one of the drawbacks of the state of theart, this invention relates to a method for distribution of cooling airfor heat-dissipating aircraft electrical equipment, the method using acooling air vein to cool at least one heat-dissipating aircraftelectrical equipment item, the said at least one electrical equipmentitem to be cooled being disposed above the cooling air vein,characterized in that the method comprises:

-   -   the formation of a first pressure zone in fluidic communication        with the cooling air vein;    -   the formation of a second pressure zone in fluidic communication        with the said first pressure zone, the second pressure zone        extending along an extension dimension greater than the        extension dimension of the first pressure zone and being in        fluidic communication with the interior of the electrical        equipment to be cooled.

The arrangement of a second pressure zone more extensive than the firstpressure zone and which communicates with the interior of the equipmentto be cooled, and particularly electronic boards thereof, makes itpossible to cool a larger portion of the equipment than in the state ofthe art.

In particular, the second pressure zone extending beneath the electronicboards to be cooled, along an extension dimension corresponding more orless to the largest dimension (length) of the electronic boards, makesit possible to distribute the flow of air drawn from the cooling airvein over the entire length of the said boards.

Therefore it no longer is necessary to design electronic boards bypositioning heat-dissipating components only in the zones situated atthe base of the cooling air vein.

The cooling air distribution method according to the invention thereforeis more effective than the methods known to date.

It will be noted that the air distributed to the electronic equipmentthen is discharged into the ambient air through openings implemented forthis purpose.

According to a possible characteristic, the second pressure zone extendsat the lower part of the electrical equipment, beneath the electronicboards to be cooled, along an extension dimension that corresponds atleast to the largest dimension of the electronic boards.

According to another possible characteristic, dependent on orindependent of the preceding one, the cooling air vein extends along afirst horizontal direction, cooling air being drawn from the air veinalong a second vertical direction, the second pressure zone extendinghorizontally.

For example, the second pressure zone extends along a third horizontaldirection perpendicular to the first direction.

It will be noted that the flow of cooling air drawn from the cooling airvein is distributed by virtue of the two pressure zones arrangedvertically one above the other. The air flow distributed in this wayalong a larger horizontal dimension (along the third horizontaldirection along which the second pressure zone extends) is distributedto the electronic boards to be cooled along a vertical axial direction,over the entire length of the electronic boards. In this way the latterare swept by the flow of cooling air from the bottom up along theirheight (this height is perpendicular to their length).

According to another possible characteristic, formation of the pressurezones comprises a step for determining a pressure drop between thecooling air vein and the first pressure zone, possibly for determining apressure drop between the first pressure zone and the second pressurezone, and possibly for determining a pressure drop between the secondpressure zone and the interior of the electrical equipment to be cooledso as to set a distribution of the cooling air.

In this way a pressure drop is determined at one and/or the other of thelevels so as to set a desired air distribution.

It will be noted that a substantial pressure drop at at least one of thelevels (for example between the air vein and the first pressure zoneand/or between the first zone and the second zone, or even between thesecond zone and the interior of the equipment) necessitates allowingmore air to pass to one and/or the other of these levels.

It will be noted that in the event of loss of forced ventilation(primary ventilated mode) originating from the avionic bay, cooling ofthe electrical equipment or equipment items by natural convection isalways possible (degraded ventilated mode).

According to another possible characteristic, the method also providesfor a filtration of the cooling air in order to separate pollutingparticles from this air, the filtration comprising:

-   -   the filtration of at least one part of the air vein by passage,        along an axial direction, through a first separation grille        between the air vein and the first pressure zone,    -   the filtration of the said at least one part of the air vein        filtered beforehand by passage, along the axial direction,        through a second separation grille between the first pressure        zone and the second pressure zone.

Each separation or filtration grill comprises a series of apertureswhich go right through the grille (in its thickness) along an axialdirection which is taken on by the cooling air in order to pass throughthe grille concerned.

It will be noted that the grilles are disposed successively one behindthe other, for example disposed in parallel.

Furthermore, the diameters of the apertures are not necessarilydifferent from one grille to the other, but of course may vary accordingto filtration needs and pressure-drop constraints.

The filtration according to the invention thus is particularly simple touse and effective.

In this way, the air drawn from the cooling vein and which isdistributed to the electrical equipment or to the electrical equipmentitems is filtered particularly effectively, which tends to reduce theproportion of dirt and dust inside the equipment or equipment items.

It will be noted that the width (or diameter) of the apertures of thesecond grille may be less than that of the first grille.

The number of apertures may vary from one grille to the other and, forexample, be greater in the second grille, the width of the aperturesalso being able to vary from one grille to the other as indicated above.

According to a possible characteristic, the method comprises filtration,by passage through a third separation grille, the said at least one partof the air vein filtered beforehand by passage through the secondseparation grille.

In this way, the filtered air originating from the second separation orfiltration grille enters the apertures of the third separation orfiltration grille so as to improve the filtration effect.

It will be noted that the third grille extends along a dimension largerthan that of the second grille/first grille or, in any case, the zone ofthe third grille provided with apertures extends along a largerdimension than the aperture zone of the second/first grille.

According to another possible characteristic, the second separationgrille comprises apertures which are offset transversely in relation tothe respective apertures of the first separation grille and/or thesecond separation grill through which the air passes along the axialdirection.

The fact that the apertures of the second grille are offset transverselyin relation to the apertures of the first grille and not opposite eachother and/or that the apertures of the third grille are offsettransversely in relation to the apertures of the second grille and notopposite each other, forms baffles for the cooling air going throughthese grilles, which becomes the air flow, thus contributing to thefiltration effect.

It will be noted, for example, that the apertures are disposed in offsetrows from one grille to the other.

The air circulating through these grilles goes through these grillesaxially but its path is deviated sideways between two consecutivegrills.

It will be noted that when a third separation or filtration grille isprovided, this additional baffle(s) level improves the filtration effecton the cooling air.

It will be noted that the axial direction of passage through the grillesby the cooling air is the direction along which the air, once filtered,passes along the electronic boards (depending on their height) and theircomponents to be cooled.

Furthermore, the transverse offset of the apertures between twoconsecutive plates or grilles may be adjusted in amplitude according tofiltration needs, while taking pressure-drop constraints into account.

According to another aspect, the invention also has as an object adevice for distribution of cooling air for heat-dissipating aircraftelectrical equipment, characterized in that the device comprises:

-   -   means for formation of a first pressure zone in fluidic        communication with a cooling air vein disposed beneath the said        at least one heat-dissipating electrical equipment item to be        cooled,    -   means for formation of a second pressure zone in fluidic        communication with the said first pressure zone, the second        pressure zone extending along an extension dimension greater        than the extension dimension of the first pressure zone and        being in fluidic communication with the interior of the        electrical equipment to be cooled.

According to other possible characteristics taken individually or incombination:

-   -   the second pressure zone extends at the lower part of the        electrical equipment, beneath the electronic boards to be        cooled, along an extension dimension that corresponds at least        to the largest dimension (length) of the electronic boards;    -   the cooling air vein extends along a first horizontal direction,        cooling air being drawn from the air vein along a second        vertical direction, the second pressure zone extending        horizontally (for example along a third horizontal direction        perpendicular to the first direction);    -   The device comprises means for filtration of at least one part        of the cooling air vein by passage, along an axial direction,        through a first separation grille between the air vein and the        first pressure zone, filtration means for the said at least one        part of the air vein filtered beforehand by passage, along the        axial direction, through a second separation grille between the        first pressure zone and the second pressure zone; such a        filtration device is particularly simple in design and proves to        be effective in filtration of the air, prior to supplying of        this filtered air to an aircraft electrical equipment item;    -   the device also may comprise means for distribution, at least in        part to the aircraft electrical equipment, of the said at least        one part of the air vein filtered by the last grille;    -   the device also may comprise means for filtration, by passage        through a third separation grille, of the said at least one part        of the air filtered beforehand by passage through the second        separation grille; the filtration grilles are disposed in        parallel so that passage of the air through each of them takes        place along the axial direction;    -   the second separation grille and/or the third separation grille        comprises/comprise apertures which are offset transversely in        relation to the respective apertures of the first separation        grille and/or the second separation grill through which the air        passes from the axial direction; this or these transverse        offset(s) form baffles for the cooling air.

According to another aspect, the invention relates to an avionic baycomprising at least one aircraft electrical equipment item and a devicefor distribution of cooling air intended to cool the said at least oneaircraft electrical equipment item.

The device for distribution of air is in accordance with the devicebriefly explained above and which may comprise the possible additionalcharacteristics mentioned above taken individually or in combination.

According to another aspect, the invention relates to an avionic bayable to accommodate one or more electrical equipment items to be cooled,the said bay using the method for cooling air distribution according tothe invention such as briefly explained above.

More particularly, the invention relates to an avionic bay comprising atleast one electrical equipment item to be cooled and a cooling air veindisposed underneath, characterized in that it comprises a first pressurezone in fluidic communication with the cooling air vein and a secondpressure zone in fluidic communication with the interior of the said atleast one electrical equipment item, the second pressure zone being influidic communication with the said first pressure zone so as to producea distribution of the cooling air in the interior of the said at leastone electrical equipment item, the second pressure zone extending alongan extension dimension greater than the extension dimension of the firstpressure zone.

The advantages linked to the avionic bay briefly explained above are thesame as those mentioned above relating to the cooling air distributionmethod according to the invention.

According to a possible characteristic, the second pressure zone extendsat the lower part of the electrical equipment, beneath the electronicboards to be cooled, along an extension dimension that corresponds atleast to the largest dimension (length) of the electronic boards.

According to another possible characteristic, the second pressure zoneis disposed in contact with a given volume of electrical equipment to becooled which is greater than the volume in contact with the sole firstpressure zone.

By virtue of an arrangement of the first and second pressure zones, itthus is possible to cool a greater volume of electrical equipment thanin the prior art.

It will be noted that in all of the foregoing, the second pressure zoneis, for example, disposed inside the electrical equipment item to becooled.

According to another possible characteristic, the bay comprises a firstseparation grille between the cooling air vein and the first pressurezone and a second separation grill between the first pressure zone andthe second pressure zone.

According to another possible characteristic, the bay comprises:

-   -   a third separation grille between the second pressure zone and        the interior of the said at least one electrical equipment item        to be cooled,    -   a rack integrating the cooling air vein, the said at least one        electrical equipment item being disposed on the rack.

According to a possible characteristic, the second separation grilleand/or the third separation grille comprise(s) apertures that are offsettransversely in relation to the respective apertures of the firstseparation grille and/or the second separation grille through which theair passes along an axial direction.

According to another possible characteristic, the bay comprises anelectrical and mechanical adaptation tray and the said at least oneelectrical equipment item to be cooled is installed on the said tray.

More particularly, the first separation grill may form part of theelectrical and mechanical adaptation tray, which simplifies the designof the bay.

According to another possible characteristic, the said at least oneelectrical equipment item may be installed on the tray through a base ofwhich the second separation grille forms part.

There again, such an arrangement simplifies the design of the bay.

More particularly, the bay comprises:

-   -   at least one electrical and mechanical adaptation tray installed        on the rack integrating the cooling air vein;    -   the said at least one removable electrical equipment item        integrating a plurality of dissipating electronic boards        installed on sliders borne by a slider support, the said slider        support being installed on a base positioned on the electrical        and mechanical adaptation tray;    -   the said electrical and mechanical adaptation tray being        provided with an aperture zone in a given zone in contact with        the air vein, the said aperture zone on the tray forming the        first separation grille for the first pressure zone.

According to other possible characteristics taken individually or incombination:

-   -   a base of the electrical equipment items bears, in the first        pressure zone which is bordered with a peripheral joint around        the aperture zone of the tray, a given distribution of apertures        and reserves of material forming the second separation grille;    -   a second peripheral joint is disposed between the base and the        aforesaid slider support so as to form the second pressure zone        in fluidic communication with at least one part of the said        first pressure zone;    -   inter-slider spaces of the aforementioned slider support are        closed off by a surface with given apertures/porosities and/or        reserves of material in fluidic communication with the second        pressure zone in order to form the third separation grille with        the interior of the electrical equipment item to be cooled.

The invention also relates to an electrical equipment item adapted forbeing installed on an avionic bay according to the invention.

Such an electrical equipment item comprises:

-   -   a slider support the inter-slider spaces of which are closed off        by a surface with given apertures/porosities and/or reserves of        material in order to form the third separation grille between        the second pressure zone, in the interior of the electrical        equipment, and the electronic boards to be cooled;    -   a base on which the slider support is positioned and which bears        a given distribution of apertures and reserves of material in        order to form the second separation grille in fluidic        communication between the second pressure zone and the first        pressure zone (for example tray and base).

The second pressure zone created between the base and the slider supportthus is intended later on, when the electrical equipment is installed ina bay, to come into fluidic communication with the first pressure zoneformed in order to ensure a distribution of the cooling air (drawn froman air vein) in the interior of the electrical equipment to be cooled.

The invention also relates to an aircraft, characterized in that itincorporates at least an avionic bay in accordance with the briefexplanation above (with or without the possible additionalcharacteristics taken individually or in partial or total combination)and able to accommodate at least one electrical equipment item accordingto the invention.

Other characteristics and advantages of this invention will be betterunderstood with the aid of the attached description and the Figures onwhich:

FIGS. 1a and 1b show views of the state of the art described above;

FIG. 2 shows a schematic view of operation of the state of the artalready described;

FIG. 3 shows a functional diagram of a device according to theinvention;

FIG. 4 shows a detail of distribution and filtration of the cooling airin the embodiment of FIG. 3;

FIG. 5 shows an illustration of a first baffle(s) level in an embodimentof the invention;

FIG. 6 shows an exemplary embodiment of a second level of baffles inanother embodiment of this invention;

FIG. 7 shows an embodiment of the invention in an ARINC 600-type avionicbay;

FIG. 8 shows a view from above illustrating the make-up of a part of adevice according to an embodiment of this invention.

FIG. 3 shows a cross section of a rack 1 of an avionic bay carried onboard an aircraft. As shown, a first pressure zone or chamber 39 isformed and is delimited by a joint 40. This joint is disposed betweenseat 7 of mechanical and electrical adaptation tray 9 and base 42 of thehousing of electrical equipment 2 to be cooled. This first pressure zoneor chamber 39 does not continue, to the right of the drawing, to thefront zone of electrical equipment 2, but on the contrary remainsconfined in the left part of the drawing near back 6 of the tray. Thearrangement of a second pressure zone allows cooling of the entirevolume 30 of the interior of electrical equipment 2.

In this way a second pressure chamber 41 is created between the upperface of base 42 of the electrical equipment and the lower face of slidersupport 43 by the interposition of a second aeraulic joint 40′. As willbe explained in detail below, slider support 43 is equipped withinter-slider zones provided with porosities or apertures 37 the diameteror diameters and the distribution of which are determined according to apredetermined pressure drop. In order to create the second pressurezone, slider support 43 is moved away from the upper face of lower base42 by crosspieces such as crosspiece 90. During installation of slidersupport 43 on the upper face of base 42, second joint 40′ is squeezedand imperviousness of the second pressure zone thus is ensured. Firstjoint 40 is tightened between seat 7 of tray 9 and the lower face ofbase 42 during insertion of electrical equipment 2 onto tray 9, bytightening of oblique nuts 45 installed on the right-hand edge of seat7. In this way imperviousness of the first pressure zone is ensured.

The distribution of cooling air throughout the volume of the electricalequipment may be designed with the aid of a software program. In orderto distribute the air, it is thus provided to:

-   -   form/create a first pressure zone in fluidic communication with        the air vein of the avionic bay;    -   form/create a second pressure zone in fluidic communication with        the said first pressure zone, the second pressure zone being        enlarged in relation to the first zone so as to extend along an        extension dimension greater than that of the first zone. More        particularly, the second zone extends, for example, along the        largest dimension of the electronic boards of the electrical        equipment (beneath same) and is in fluidic communication with        the interior of the electrical equipment to be cooled. The        largest dimension of the equipment is that which includes the        largest longitudinal dimension or length of the electronic        boards.

It will be noted that the first zone extends only over a part of thelargest dimension of the equipment and therefore of the length of theboards.

Fluidic communications are determined in particular by the dimensioningof porosities or apertures 34 (zone 17 of the seat) and 35 (zone 19 ofbase 42) with diameters and distribution different from one zone to theother.

It will be noted, however, that the diameters of apertures 34 and 35 arenot necessarily different. Furthermore, the dimensioning anddistribution of apertures 37 of slider support 43 determine the fluidiccommunication between the second zone and the interior of the equipment.It will be noted that the diameters of apertures 37 and 35 are notnecessarily different.

The result of the foregoing is that the air coming from cooling air vein14 goes through, under a pressure drop determined by the porosity of theapertures, first zone 17 of apertures 34 in order to fill first pressurechamber 39 delimited by joint 40. Then air under pressure (36) goesthrough a second zone 19 of apertures 35, arranged in base 42 of thehousing for the equipment, and is delivered throughout the volume ofsecond pressure chamber 41. Finally, the air is distributed (38) tovolume 30 to be cooled (boards and components) in electrical equipment 2through apertures 37 arranged in slider support 43. The precedingarrangement thus makes it possible to deliver/distribute cooling air inthe entire zone 30 occupied by the electronic boards in operation.

The air filtration effect obtained by the various series or successivelayers of apertures of the separation or filtration grilles now is goingto be described with the aid of FIG. 4.

FIG. 4 illustrates an exemplary air distribution/filtration deviceaccording to the invention.

Rack 1 bears seat 7 of the mechanical and electrical adaptation traywhich is provided with apertures 51 and constitutes a first separationor filtration grille. The distribution and number of apertures 51 isdetermined by the pressure drop that is wished to be imposed on gaseousvein 14 in order to pressurize first pressure chamber 39. For thispurpose, the arrangement of joint 40 around perforated zones 17 and 19is noted. Base 42 has a series of apertures 53-55 the axial (vertical)drilling axes of which are offset transversely (horizontally) inrelation to the axial drilling axes of at least some apertures 51 offirst grille 7. The base provided with apertures 53-55 constitutes asecond separation or filtration grille. When the air under pressure goesthrough apertures 51 from the bottom upward, the offset of the axes ofthe apertures and the difference between the number of apertures infirst grille 7 and in second grille 42 (it will be noted that thisdifference in number of apertures is optional) make it possible to breakup the air jets originating from apertures 51 and to diffuse the airhomogeneously to apertures 53-55 of base 42. The offset of aperturesbetween the two grilles leads the air to follow a deviated (winding) andnot straight course, forming as it were one or more baffles for the flowof air going through the first grille and getting back to the secondgrille to go through it. This offset arrangement ensures a protectionagainst possible polluting particles in suspension in the air. Apertures51 make it possible to distribute the pressure in chamber 39 in order tocome to pressurize it. When an air jet originates from an aperture 51,it has a tendency to break up on the lower face of base 42, at a placedisposed opposite (axially) the emerging end of aperture 51, a placewhere the second grille has no apertures (on the contrary, at this placethe second grille has a given reserve of material). This offsetarrangement makes it possible to have any polluting particles trapped invein 14 fall down again, which particles otherwise could be introducedinto the electrical equipment to be cooled. In this way, a purified andfiltered air passes through apertures 53, 54, 55 of second grille 42.The same distribution of offset apertures is applied to the third seriesof apertures 56-58 which are distributed over the entire surface ofslider support 43 (third filtration grille). This offset arrangementintroduces a second step of filtration of the cooling air by creating,as between the first and second grilles, a baffle(s) effect.

As shown on FIG. 4, the air going through the apertures of second grille42 generally follows a more winding course to get back to the aperturesof third grille 43 than the air passing from the apertures of the firstgrille to those of the second grille. This is explained by the fact thatthe apertures of the third grille are distributed over a far moreextensive zone than zone 19 of the second grille. Since the air flow ismore markedly deviated, the filtration effect thereof is increased. Theapertures of the second and third grille are, for example, equal in sizebut not necessarily in number.

It will be noted that in a variant, the zone of the third series ofapertures possesses the same dimensions as zone 19 of the second seriesof apertures.

According to another variant, the third filtration grille is omitted.

When the electronic boards are used in a damp ambient environment,polluting particles, in particular metal particles contained in the airvein and which are carried along by the forced ventilation system of theairplane, may adhere to the conductive paths of the electronic boardsand constitute short-circuits of sorts between the paths of the boards.These short-circuits lead to electrical malfunctions. In order toovercome this phenomenon, some parts manufacturers put down varnish onthe electronic boards so that the paths of the board are insulated fromshavings possibly projected onto same. However, this involves severaldesign disadvantages. In fact, it is necessary to perform additionalvarnishing operations during manufacture of the electronic boards, whichis going to lead to additional costs. Furthermore, when it is wished torepair a board, it first is necessary to perform a de-varnishingoperation in order to access the conductive paths. Finally, certainproducts used on the electronic boards are incompatible with theinsulating varnishes used, for example the layers of silicone-basedthermal coupling.

By filtering the largest particles at the bottom part of the electricalequipment, projection of these particles onto the boards thus islimited. To implement such a solution, a dual-baffle concept with threelevels of filters is used as follows:

-   -   a very porous lower base 42 (second filtration grille)        nonetheless with closings directly facing the ventilation        apertures of seat 7 (first filtration grille) of the electrical        and mechanical adaptation tray; this first baffle level is        intended to retain the largest particles between the bottom of        rack 1 and base 42 of electrical equipment 2;    -   a slider support 43 (third filtration grille) opposite lower        base 42 (second grille) very clearly less porous than seat 7 of        the tray so as to generate a pressure drop with apertures 56-58        still offset in relation to apertures 53-55 of lower base 42.        This offset may be implemented in two ways:    -   either at slider support 43,    -   or through local closings on the slider support, which is porous        facing the apertures of the inter-slider spaces. This second        level of baffles is intended to trap the large particles which        might have been able to pass the first barrier of baffles        between base 42 and ARINC tray seat 7.

On FIG. 5, a diagram of distribution between the different porosities ofthe two first levels of baffles provided has been shown in a view fromabove. ARINC tray seat 7 is equipped with a peripheral joint 60 and withapertures 61 distributed over the entirety of first pressure zone 39visible on FIG. 2. Above this perforated plate or grille, there isdisposed the porous base of the equipment comprising a plurality ofsmall apertures 63 which are offset in relation to any aperture 61 ofthe seat (apertures 61 are seen showing through in order to facilitateunderstanding). Apertures 63 are arranged between apertures 61 along aprojection view on the seat of the tray. Porous base 62 of the equipmenthas apertures only in the zone surrounded by joint 60 so as to allow acommunication exclusively with first pressure chamber 39.

FIG. 6 illustrates an embodiment of two levels of baffles. Joint 60 andporous base 62 with its apertures 63 have been shown again. Slidersupport 64 is disposed above the second pressure chamber. Slider support64 is provided with a series of apertures 65 contained in widened zone67, and which are disposed above apertures 63 of base 62 of theequipment, but in offset manner. Apertures 65 also extend in a zone thatis offset laterally in relation to the zone of the seat delimited byjoint 60.

The result of this arrangement is that the air under pressure may passfrom first pressure chamber 39 to second pressure chamber 41, thusmaking it possible to diffuse the air in the interior of the equipmentin a zone 67 with larger expanse than delimited zone 60 available bydefault in the avionic bay.

On FIG. 7, an embodiment of the device of the invention has been shownschematically in a view from above. The seat (delimited zone 60) of theARINC tray and lower porous base 62 of the equipment that serves tosupport the sliders for the boards thus are discerned. In this stacking,sliders 75 and perforated inter-slider zones 74 for cooling theelectronic boards may be seen. Joint 40′ between the base and the slidersupport is disposed in a maintenance groove of the base. Ventilationapertures 72 are disposed both in the inter-slider zones such as zone 74and outside ARINC zone 60 but are not arranged facing the apertures ofthe porous lower base. Reserves of material 71 also have been providedon the porous lower base so that the main apertures of the seat of theARINC tray do not directly face the apertures of the base of theequipment.

FIG. 8 is a view from above of the porous lower base which is disposedabove the seat of the ARINC tray. This porous lower base 42 comprises anaperture or porosity zone 82 disposed above aperture zone 81 implementedin the seat of the ARINC tray. Aperture zone 82 is delimited by thelimitation joint of first pressure chamber 39 so that the apertures ofzone 82 allow a controlled fluidic connection between the first andsecond pressure zones.

Material reserve zones 83 and apertures 84 have been shown on lower base42. Material reserve zones 83 are situated facing ventilation apertures85 of the tray seat. These zones 83, however, also may be placed facingthe ventilation apertures of the slider-holder plate or slider support43 (not shown on FIG. 8).

The taking into consideration of the constraints of pressure drop whichthe electrical equipment imposes results directly in a porosity, or adegree of porosity, determined for each of the three levels ofseparation of filtration grilles. It will be noted that the low porosityvalues (small diameters) of the separations or grilles may create highlocal speeds, potentially generating interference in the pressure-flowoperating range. These interferences are uncomfortable for the crew andthe passengers on board the aircraft. These acoustic phenomena areintensified when the ventilation system generates:

-   -   high-speed air jets in the equipment,    -   abrupt variations between passage areas between the electronic        bay and the equipment access.

It thus is provided to offer a more gradual variation of theseparations, between the ARINC tray and the porous lower base on the onehand, and between the porous lower base and the slider support on theother hand, the porosity of which then may be increased. By increasingthe porosity for the same flow, air speeds may be reduced.

It will be noted that the obstacles resulting from the dual-baffleconcept favorably disturb the flow of the air, thereby attenuating theacoustic phenomena of whistling and/or resonant cavity. By adjusting thevarious degrees of porosity and the distributions of material reservesat the time of design, it is possible to obtain:

-   -   a function of distributor of air over the lower surface of the        equipment,    -   an optimization of forced convection performance during        ventilated conditions but also when the ventilation is out of        order and one goes over to natural convection;    -   filtration of the most voluminous impurities by virtue of the        concept of three porosity levels.

During ventilated conditions, gains are obtained ranging between:

-   -   0 and 10° C. temperature lowering depending on the components        and the electronic boards with an average value on the order of        3° C. in ventilated conditions over average temperature rises of        15 to 25° C. This comes down to being able to evacuate an        additional dissipated thermal power ranging between 12 and 20%        in comparison with the state of the art.    -   from 0 to 5° C. temperature lowering on cutoff of ventilation,        with an average value of 1 to 2° C. depending on the electronic        boards and the components;

Over temperature rises of 35 to 40° C., the average gain in dissipatedthermal power is 2.5 to 6% and over average temperature rises of 25° C.,the average gain in dissipated thermal power is 4 to 8%.

It has been noted following tests that:

-   -   on a type-3MCU equipment item, an increase in porosity of 78% on        the slider-holder plate with joint (slider support) outside the        first pressure chamber is expressed simply by a flow increase        between 40 and 45% over the pressure range tested;    -   on a type-6MCU equipment item, an increase in porosity of 42% on        the slider-holder plate with joint outside the zone of the first        pressure chamber is expressed simply by a flow increase of 15 to        20% over the pressure range tested.

By determining the degrees of porosity of the three grilles orseparations beforehand, a more effective distribution of cooling air maybe provided in normal forced convection mode as well as in degradednatural convection mode.

The invention claimed is:
 1. A method for distribution of cooling airfor heat-dissipating aircraft electrical equipment, the method using acooling air vein configured to introduce air to cool theheat-dissipating aircraft electrical equipment, the heat-dissipatingaircraft electrical equipment to be cooled being disposed above thecooling air vein, the method comprising: forming a first pressure zonein fluidic communication with the cooling air vein; forming a secondpressure zone in fluidic communication with the first pressure zone, thesecond pressure zone having an extension dimension extending along anextension dimension greater than an extension dimension of the firstpressure zone and being in fluidic communication with an interior of acompartment configured to house the heat-dissipating aircraft electricalequipment to be cooled; filtering at least one part of the cooling airby passage, along an axial direction, through a first separation grillebetween the cooling air vein and the first pressure zone; filtering saidat least one part of the cooling air filtered beforehand by passage,along the axial direction, through a second separation grille betweenthe first pressure zone and the second pressure zone; and filtering saidat least one part of the cooling air by passage through a thirdseparation grille, said at least one part of the cooling air beingfiltered beforehand by passage through the second separation grille,wherein the first pressure zone is downstream of the cooling air vein,and the second pressure zone is downstream of the first pressure zoneand the cooling air vein, and wherein the third separation grille isarranged upstream of and disposed below a portion of the interior of thecompartment configured to house the heat-dissipating aircraft electricalequipment to be cooled.
 2. The method according to claim 1, wherein thesecond pressure zone extends at a lower part of the heat-dissipatingaircraft electrical equipment, beneath electronic boards of theheat-dissipating aircraft electrical equipment to be cooled, along theextension dimension, which corresponds at least to a largest dimensionof the electronic boards.
 3. The method according to claim 1 or 2,wherein the cooling air vein extends along a horizontal direction,cooling air being drawn from the cooling air vein along a verticaldirection, and the second pressure zone extending horizontally.
 4. Themethod according to claim 1, wherein said forming the first and secondpressure zones is based on determining one or more of a pressure dropbetween the cooling air vein and the first pressure zone, determining apressure drop between the first pressure zone and the second pressurezone, and determining a pressure drop between the second pressure zoneand the interior of the heat-dissipating aircraft electrical equipmentto be cooled, so as to set a distribution of the cooling air.
 5. Themethod according to claim 1, wherein one or more of the secondseparation grille and the third separation grille includes aperturesthat are offset transversely in relation to respective apertures of oneor more other separation grilles of the first separation grille, thesecond separation grille and the third separation grille, through whichthe cooling air passes along the axial direction.
 6. An avionic baycomprising: electrical equipment to be cooled; and a cooling air vein,disposed underneath the electrical equipment, to provide cooling air; afirst pressure zone in fluidic communication with the cooling air veinto receive the cooling air from the cooling air vein; a second pressurezone in fluidic communication with an interior of a compartmentconfigured to house the electrical equipment; a first separation grilledisposed between the cooling air vein and the first pressure zone; asecond separation grille disposed between the first pressure zone andthe second pressure zone; and a third separation grille disposed betweenthe second pressure zone and a portion of the interior of thecompartment configured to house the electrical equipment, wherein thesecond pressure zone is in fluidic communication with the first pressurezone so as to produce a distribution of cooling air in the portion ofthe interior of the compartment configured to house the electricalequipment, the second pressure zone extending along an extensiondimension greater than an extension dimension of the first pressurezone, wherein the first pressure zone is downstream of the cooling airvein, and the second pressure zone is downstream of the first pressurezone and the cooling air vein, and wherein the third separation grilleis arranged below the portion of the interior of the compartmentconfigured to house the electrical equipment to be cooled.
 7. Theavionic bay according to claim 6, wherein the second pressure zoneextends at a lower part of the electrical equipment, beneath one or moreelectronic boards of the electrical equipment to be cooled, along theextension dimension, which corresponds at least to a largest dimensionof the one or more electronic boards.
 8. The avionic bay according toclaim 6 or 7, wherein the second pressure zone is disposed in contactwith a given volume of the electrical equipment to be cooled, which isgreater than a volume of the second pressure zone in contact with thefirst pressure zone.
 9. The avionic bay according to claim 6, furthercomprising: a rack integrating the cooling air vein, the electricalequipment being disposed on the rack.
 10. The avionic bay according toclaim 9, wherein one or more of the second separation grille and thethird separation grille includes apertures that are set off transverselyin relation to respective apertures of one or more of the other grillesthrough which the cooling air passes along an axial direction.
 11. Theavionic bay according to claim 6, further comprising an electrical andmechanical adaptation tray, the first separation grille forming a partof the adaptation tray, and the electrical equipment being installed onthe adaptation tray, the electrical equipment being able to be installedon the adaptation tray, over a base, of which the second separationgrille forms a part.
 12. An aircraft comprising at least one saidavionic bay according to claim
 6. 13. The avionic bay according to claim6, wherein a first aeraulic joint forms the first pressure zone and asecond aeraulic joint forms the second pressure zone.
 14. The avionicbay according to claim 6, wherein the avionic bay is configured to havea pressure drop at one or more of an interface between the cooling airvein and the first pressure zone, an interface between the firstpressure zone and the second pressure zone, and an interface between thesecond pressure zone and an interior of the electrical equipment. 15.The method according to claim 1, wherein the first pressure zone definesa first volume and the second pressure zone defines a second volume, thesecond volume being greater than the first volume.
 16. The methodaccording to claim 1, wherein the third separation grille has a lengthin the extension dimension greater than a length of at least one of thefirst separation grille and the second separation grille in theextension dimension.
 17. The method according to claim 1, wherein thefirst separation grille is below the second separation grille, and thesecond separation grille is below the third separation grille.
 18. Theavionic bay according to claim 6, wherein the third separation grillehas a length in the extension dimension greater than a length of atleast one of the first separation grille and the second separationgrille in the extension dimension.
 19. The avionic bay according toclaim 6, wherein portions of the first separation grille, the secondseparation grille, and the third separation grille overlap in an axialdirection orthogonal to the extension dimension.